The primary objective of this investigation is to determine if human cholesterol gallstones can be dissolved by oral administration of either of the primary human bile acids, cholic or chenodeoxycholic acid. Previous work by the principal investigator has shown that the abnormal bile composition of patients with cholelithiasis can be corrected by chenodeoxycholic administration, that chenodeoxycholic acid is without apparent toxicity, and that administration of chenodeoxycholic acid for one year to two patients was associated with 80 percent reduction of gallstone size in one. Because of these promising results and because of the desirability of a medical treatment for cholelithiasis, support is sought for a controlled therapeutic trial involving sufficient patients to define the efficacy of this treatment. Forty-five women and fifteen men with radiolucent gallstones (and functioning gallbladders) will be allocated to receive cholic acid or chenodeoxycholic acid or placebo for a period of two years. An additional five women and five men with radiopaque gallstones (and functioning gallbladders) will also receive chenodeoxycholic acid for two years. Gallstone size will be assessed by standardized cholecystograms with tomograms initially and at 6 month intervals. Laboratory tests will be carried out at similar intervals to detect any effect of the drug on serum lipids or hepatic function. Duodenal bile, obtained at the beginning, one year, and end of the study will be analyzed to document induced alternations in bile composition; changes in biliary bile acid composition will be used to confirm bile acid ingestion. A second objective of the study is to define cholesterol kinetics in patients with cholesterol cholelithiasis and the influence of bile acid ingestion on these. Six subjects from each group will receive cholesterol-C14 six months after beginning treatment and the serum cholesterol specific activity decay curve determined to estimate pool size and turnover rate as described by Goodman and Noble.